Sign up to take Mensa's IQ test at the group's website. You'll receive testing information for your area. The Mensa test costs $40 as of time of publication, and you must be at least 14 to take it.
Consider taking practice tests at home, even though the Mensa test is an intelligence test, not an aptitude exam such as the SAT. The practice test might help if you're uncomfortable with standardized tests. For $18 -- as of time of publication -- Mensa will send you a practice test. You can also take the practice test online. You might also find other free online IQ tests for practice.
Prepare yourself. You can't cram for an IQ test by studying, but be sure to get good sleep and eat a healthy meal.
Wait for your test results. Unfortunately, Mensa doesn't tell you your actual intelligence test scores. They just tell you if you're in the top 2 percent.
Become a Mensa member, or a member of your local Mensa chapter. Chapters have regular events where you can meet other Mensans in your area.